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HDMI

Posted by Eric Smith on

Quick Guide: HDMI and HDMI cables

What is HDMI? HDMI stands for High-Definition Multimedia Interface, and that's a pretty good description of what it is. In layman's terms, HDMI is a type of digital connection that's capable of transmitting high-definition video and high-resolution audio over a single cable. To do the same thing with analog cables, you'd need to connect three component-video cables plus six analog audio cables--that's a whole lot of cable clutter. HDMI is typically used to connect a high-definition device--such as an HD DVR--to an HDTV. To make the connection, you simply put one end of the cable into the HDTV's HDMI input slot and the other end into the device's HDMI output slot. And that's it--just one cable and you're all set for the high-definition experience. If you have an AV receiver, just put it in the middle of the signal chain. The output of the AV receiver goes to the HDTV and you connect your high-definition device(s) to the AV receiver's input. How does it compare to other cable types? HDMI can deliver the best image quality of any of the cable types available today. It can handle high-definition video of up to 1080p resolution at 60 frames per second, which is the most bandwidth-intensive video format currently available. The older PC-based DVI connection offers equivalent quality, but it is rarely available on HDTVs or video components these days. Component video is found on nearly all electronics that output high-def video, and its image quality is slightly lower than HDMI, but it's really difficult for most people to tell the difference. Many viewers are probably familiar with the quality associated with the various standard-definition video cables--namely S-Video, composite (the yellow video cable), and RF--and HDMI provides a potentially huge improvement over all of them. As always, however, the biggest factor in video quality is the source; a low-quality source delivered over HDMI will still look worse than a high-quality source over S-Video. For audio, HDMI is the reigning king of quality as well. It supports the ability to carry eight channels of 24-bit audio at 192kHz--enough to handle even the highest resolution audio soundtracks such as Dolby TrueHD and DTS-HD Master Audio. The only other connection type that can deliver the same quality are multichannel analog audio cables, but you'd need to run as many as eight separate cables to get the same quality. Digital audio cables--both optical and coaxial--can deliver multichannel audio, but are limited to lower-resolution audio signals HDMI versions One of the most confusing aspects of HDMI is that there are several different versions. While most new products support HDMI 1.3, many older products support older HDMI iterations, such as HDMI 1.2. Much has been made about HDMI 1.3 and its increased bandwidth, but it offers few real-world benefits. Yes, it adds support for "Deep Color"--which is an expanded color gamut--but outside of a few high-def camcorders, there aren't any sources that actually use Deep Color. There are no current or announced Blu-ray discs that use Deep Color. HDMI 1.3 also adds automatic lip-syncing, but we haven't had any problems with lip-syncing on previous HDMI versions. The major upgrade for HDMI 1.3 was that it enables the ability to send high-resolution soundtracks such as Dolby TrueHD and DTS-HD Master Audio in bit stream format. While all HDMI versions can handle these soundtracks if they've first been converted to PCM format by a compatible player, HDMI 1.3 is needed if they are to be sent in encoded bit stream format. It's certainly counterintuitive--since these soundtracks are actually losslessly compressed in bit stream format and therefore require less bandwidth--but that's the way it works. This feature is also likely to become much less important as new Blu-ray players with onboard decoding for all high-resolution soundtracks become available. Currently, with the latest version, HDMI 1.4a support for 3D, higher resolution (up to 4K), and Ethernet transmission are the key benefits. Content Protection - HDCP Would it be possible for HDMI to have so much support from the motion picture industry if it didn't offer upgraded security over its predecessors? Probably not, which is why HDMI has licensed High-bandwidth Digital Content Protection or HDCP. Created by Intel subsidiary Digital Content Protection , LLC, HDCP is required on HD-capable set-top boxes that use HDMI. It is also used with players that can output HD content like a Blu-ray disc player, an upscaling DVD player, or high resolution gaming system.. Since HDCP is a proprietary technology it requires a license to be implemented on a device. As part of the agreement a licensee has to limit the output capabilities from all non-HDCP video outputs if requested by the source. This means in effect that the quality of video output will be lowered dramatically through a non-HDCP compliant output. This downgrade in quality (outputting standard resolution instead of the sought high definition resolution) is being done to protect high definition content from theft. (See the article"The Analog Sunset" in the Learning Center ) HDCP works by encrypting the digital content being sent from the source to the receiver(s) through either HDMI or HDCP-enabled DVI connections. Using HDMI's DDC channel, the source and receivers initiate a "handshake" and validate that each device is an authorized one. During this process, each exchanges a special key called a Key Selection Vector or KSV. Each HDCP-enabled device has 40 unique keys (the KSV is created from the set) and if these keys are not kept confidential, the license agreement is broken. During this process the Keys and KSV's are generated in a way that ensures each device gets the same 56 bit number which is used in the encryption process. A XOR operation is applied to encrypt each decoded pixel with a 24-bit number. HDCP requires constant updating of keys to ensure security. If a model is considered compromised (hacked) then the KSV is added to a dreaded revocation list. New HD discs would include this list. If a source devices finds a receiver's KSV on the list, it will not send protected HD data to it. The revocation list is protected to ensure that a malicious user couldn't revoke an uncompromised device. Why HDMI? - What Are The Advantages Here are the main advantages of using HDMI... • All-Digital - HDMI transmits All-Digital data, which means video content will not have to suffer unnecessary digital-to-analog conversions and puts an end to analog interfere problems. • Video & Audio Quality - Utilizing its available 10.2Gbps of bandwidth, HDMI can easily transmit uncompressed 1080p video content with multi-channel audio content, ensuring the highest possible playback quality from your display device / sound system. • Intelligent Features - HDMI brings intelligence to a system through DDC and CEC. This allows for such advanced features as "automatic format adjustment" and "one touch control". • HDCP - In the future, protected digital broadcasts like Pay-Per-View and High Definition movies on next generation discs will require HDCP-enabled equipment to protect the content. While having a new content protection technology doesn't seem too interesting or beneficial to the consumer, it is alarming to know that lacking HDCP in your equipment might leave you with downgraded video quality (standard resolution video) or possibly, in cases, no playback at all. (See the article"The Analog Sunset" in the Learning Center ) • Future-proof - HDMI is an evolving technology and could already, for example, support video content with a higher resolution than 1080p and improved color reproduction. • Ease-of-use - HDMI can do in one cable what could take several cables otherwise. There are many many more benefits to using HDMI but these are the advantages that are most important to a consumer.

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